Paleomagnetism and accretionary tectonics of northern Sikhote Alin

摘要

The results of the paleomagnetic investigation of the sediments pertaining to the Silasinskaya Formation of the Kiselevka-Manoma terrane within the Sikhote Alin orogenic belt are presented. The ancient prefolding magnetization component is revealed: Decs = 271.7A degrees, Incs = 52.2A degrees, Ks = 13.5, and a (95s) = 5.1A degrees (positive fold and reversal tests); and the coordinates of the corresponding paleomagnetic pole for 103 +/- 10 Ma are calculated: Plat = 26.3A degrees, Plong = 70.5A degrees, dp = 4.8A degrees, and dm = 7.0A degrees. As a result of this study, the geodynamical settings and paleolatitudes of the formation of three objects in the northern part of Sikhote Alin orogen are established: (a) the Kiselevskaya Formation of the Kiselevka-Manoma terrane was formed 133 Ma ago at 19A degrees N under the seamount condition on the Izanagi Plate; (b) the Silasinskaya Formation of the Kiselevka-Manoma terrane was formed 103 Ma ago at 35A degrees N under the oceanic island arc conditions; and (c) the Utitskaya Formation of the Zhuravlevsk-Amur terrane was formed 95 Ma ago at 54A degrees N in the active continental margin conditions. It is found that the transform continental margin of Eurasia developed in the time interval from 105 to 65 Ma ago in the regime of a left-lateral submeridional shear from 30A degrees to 60A degrees N. The complete attachment of the studied rocks of the Kiselevka-Manoma terrane to the Eurasia's margin (to the Zhuravlevsk-Amur terrane) occurred at the boundary of 60-70 Ma. Simultaneously, the sense of the displacement in the submeridional shears changed from left-lateral to right-lateral with the formation of pullapart type basins (Lake Udyl').